The invention is directed generally to a surgical method, and more specifically to a composition for use during ophthalmic surgery.
In the eye, the cavity between the lens and the retina is filled with a clear, jelly-like semisolid substance termed the vitreous body or vitreous. Its volume is fixed and is relatively permanent. The vitreous is surround by the hyaloid membrane. In pathological conditions such as macular hole, vitreomacular traction syndrome and proliferative vitreoretinopathy, the posterior cortical vitreous (posterior hyaloid) is partially or completely attached to the retina and the inner limiting membrane and thus may provide a source of traction. The attachment may also serve as a scaffold for fibrous proliferation in proliferative diabetic retinopathy.
Proliferative vitreoretinopathy, a major cause of failure of retinal reattachment surgeries, involves cellular proliferation on the anterior and posterior surfaces of the retina. Cellular vitreous strands and membranes form and contract, creating a new retinal detachment and usually loss of some vision. Both clinical and experimental evidence suggests that breakdown of the blood-retinal barrier is important in the pathogenesis of proliferative vitreoretinopathy, stimulating basic cellular processes of growth, chemotaxis, migration, and proliferation. This loss of blood retinal barrier integrity results in an increase in the protein content of intraocular fluid, which may stimulate intraocular fibrin formation and creation of a scaffold of preretinal cellular membranes. These membranes subsequently contract to create a tractional retinal detachment typical of proliferative vitreoretinopathy.
A patient suffering from any of these conditions may undergo a surgical procedure, such as pars plana vitrectomy, in an attempt to alleviate these conditions. However, the surgical procedure itself also produces complications. Postoperative intraocular fibrin formation is a common complication of vitrectomy surgery and penetrating ocular injury. Extensive intraocular surgery, epiretinal membrane dissection in proliferative vitreoretinopathy, and inflammatory conditions such as endophthalmitis and uveitis exaggerate postoperative intraocular fibrin formation because of increased vascular permeability. Additional surgical procedures such as endophotocoagulation, cryopexy, scleral buckling, and intraocular gas introduction also exacerbate the intraocular inflammation. Various other factors have been implicated in fibrin formation including a preoperative retinal detachment, combined surgery (lensectomy and vitrectomy), and severe or prolonged hypotony. Eyes with proliferative diabetic retinopathy are especially susceptible to fibrin formation because long-term disease damages the blood retinal barrier. Laser and cryopexy have been shown experimentally to compromise the blood retinal barrier, enhancing the ability of the vitreous to stimulate retinal pigment epithelium migration and proliferation, thereby increasing the incidence of tractional retinal detachment. Additionally, a high percentage of surgeries fail in severely diseased, previously operated, and uveitic eyes, and effective treatment of retinal detachment with a proliferative vitreoretinopathy component, severe proliferative diabetic retinopathy with traction retinal detachment, and persistent ocular inflammatory disease remain a challenge for vitreoretinal specialists.
During surgery the transparency of vitreous makes it difficult for the surgeon to visualize and hence completely remove the vitreous and posterior hyaloid. A surgeon performing a procedure may not be absolutely certain whether posterior hyaloid separation and complete vitrectomy has occurred. Many surgical techniques have been described which attempt to aid in removal of the posterior hyaloid during pars plana vitrectomy. These include the use of various cannulas and forceps with active or passive suction applied to engage and separate the posterior hyaloid from the retina. New drug delivery devices have improved surgical outcomes and controlled intraocular inflammation. Also, Ryan et al. have described the use of autologous blood for improved visualization of cortical vitreous during posterior hyaloid separation. None of these are completely satisfactory, however, and use of blood has several drawbacks: blood disperses into the vitreous cavity and is likely to obscure visualization during vitrectomy, and has the potential of causing postoperative inflammation and proliferative vitreoretinopathy.
A need still exists for surgical correction of the defect, but with improved accuracy and precision so that complications, as well as reduced discomfort, inconvenience and expense to the patient, may be minimized. Thus, methods and agents to improve the visualization of the vitreous during a surgical procedure, and hence to ensure accuracy of the procedure, are desirable to achieve better functional and anatomical outcomes.
The invention is directed to a method to alleviate a structural disorder of an eye. A vitreous delineating agent is injected into the eye in an effective amount to allow the vitreous to be visible to a surgeon, enabling the surgeon to alleviate the disorder. The agent may be a therapeutic agent, an inert agent, or an inert agent that contains a therapeutic agent, such as a microsphere or liposome containing a therapeutic agent. In one embodiment the agent is a corticosteroid but may be, for example, an antiinfective agent, an immunosuppressant agent, an antiproliferative agent, and/or an antiangiogenesis agent. The agent may be in a formulation such as a solution, an emulsion, or a suspension.
The invention is also directed to a method to alleviate a structural disorder of an eye by injecting a corticosteroid formulation into the eye in an effective amount to enable a surgeon to visualize the vitreous and to thus alleviate the disorder. The corticosteroid formulation may also contain an additional therapeutic agent, and/or may be incorporated into a vesicle such as a microsphere or a liposome.
The invention is additionally directed to a composition for visualizing a vitreous cavity in a mammalian eye during surgery. The composition is an injectable formulation of a vitreous delineating agent that associates with vitreous fibers in the eye to render the vitreous cavity visible to the surgeon. The formulation of the agent may be translucent, opaque, or semi-opaque.
These and other aspects of the invention will be apparent in light of the following figures and detailed description.